In the case of the uses of fishing nets such as purse seines, towing nets, stationary nets, gill nets, longlines, nets used to define fish preserve or culture and so on, in general, buoys are fastened to predetermined positions of the fishing nets in order to identify the positions of the fishing nets and to maintain the fishing nexts in water in a desired shape.
In order to enable the visual perception of such buoys at night, reflecting elements are attached to the surfaces of the buoys or storage type fluorescent materials are coated over the surfaces of the buoys.
However, the buoys with the reflecting elements attached to the surfaces thereof have the following problems.
That is, the reflecting elements are only bonded to the surfaces of the buoys, they tend to be easily separated from the buoys when the buoys are thrown into water and when they collide against the hull of the ship vessels as they are retrieved on the ships or against drifts. They are also separated due to friction. Furthermore, in order to visually perceive such buoys, light sources must be provided in order to emit the light rays which in turn are reflected by the reflecting elements. In addition, the visual perception distance is limited by the capacity or intensity of the light sources. Moreover, when the buoys move or the ships pitch, roll and rock, it becomes impossible to correctly strike the light rays against the reflecting elements so that it sometimes becomes very difficult to find out the buoys with the reflecting elements.
Meanwhile, the storage-fluorescent-material coated buoys also have some problems to be described below.
That is, since the fluorescent materials are only coated over the surfaces of the buoys, they also tend to be separated as in the case of the buoys with the reflecting elements. Furthermore, in order to store the energy into the fluorescent materials, the light sources are also needed. In addition, their light-emission time is short and its maximum luminance is low so that the distance at which the buoys can be perceived is extremely limited. Moreover, their luminance decreases as time elapses so that it becomes difficult to perceive them. The luminance of a fluorescent material is in general in proportion to the intensity of light emitted from a light source so that when the light rays are emitted from a distance spaced by some distance from a buoy in order to make the luminance of the buoys perceivable, a light source having a relatively high light-emitting capacity is needed. As a result, the cost is increased and a light source used is increased in size the weight so that a relatively large space for installation of a light source must be provided on a ship.